Flexible structure orientation control

ABSTRACT

Separated parts of a flexible structure are maintained in a predetermined desired orientation with respect to each other against the action of distorting forces by applying to selected part or parts of the structure inertially developed torques (e.g. from flywheels) to main the selected part in its desired orientation with respect to a selected reference part of the structure.

United States Patent Philip D. Holthenrichs Malvern;

Robert P. Wanger, Valley Forge, Pa. 794,874

Jan. 29, 1969 May 25, 1971 General Electric Company Inventors Appl. No.Filed Patented Assignee FLEXIBLE STRUCTURE ORIENTATION CONTROL PrimaryExaminer-Henry C. Sutherland 3 Claims, 9 Drawing Figs- Attorneys-WilliamG. Becker, Paul F. Prestia, Allen E. vs. C1 52/1 Amgm Henry Kaufman,Frank Neuhauser, Oscar 52/173, 343/706 B. Waddell and Melvin M.Goldenberg Int. Cl Fl6f 7/00,

F16f 15/30, F04h 12/00 0f Search Se arated parts fa flexible tructureare main- 188/1; 244/1 (SS); 343/700, 704, (Dlge t l) tained in apredetermined desired orientation with respect to 7045 each otheragainst the action of distorting forces by applying f to selected partor parts of the structure inertially developed Re cream torques (e.g.from flywheels) to main the selected part in its UNITED STATES PATENTSdesired orientation with respect to a selected reference part of3,276,024 9/1966 Stevens 343/7045 the structure.

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INVENTORS ROBERT F. WANGER, PHIL/P D. HOLTHE/VR/CHS,

AMP.

AGENT FLEXIBLE STRUCTURE ORIENTATION CONTROL BACKGROUND OF THE INVENTION1 Field of the Invention This invention pertains to the use of poweredmeans to control the deflections of portions of flexible structures.

2. Description of the Prior Art The oldest and most general approach tocontrolling the deflections of separated portions of flexible structureshas been to make the structures more rigid, and thus less subject todeflection, either by making their members larger, or using materials ofhighermoduli of elasticity, or by altering their geometry to make themstiffer, or by a combination of any of these. A slightly moresophisticated approach is to modify the structure to cause smallerforces to be applied to them by the source of the deflecting force, asby' shaping a mast to offer less resistance to the wind.

Specialized schemes have included provision of means to change thelengthsof various members in order to restore the desired conformationwhich has been altered by distorting force.

The older schemes have the disadvantage that they add weight or cost tothe structure, or restrict the permissible conformations which may beused. They in effect destroy any inherent great flexibility which may bea very useful characteristic of the structure at some time in its useother than the time when rigidity is desired.

SUMMARY OF THE INVENTION Our invention provides for the application, toselected part or parts of the flexible structure whose deflection is tobe controlled, of a torque appropriate to negate or damp thatdeflection. This we accomplish by inertial means, since the use of anymeans requiring some rigid reference frame against which to thrustwould, ashas been indicated, defeat our purpose. In general, we employsuitable deflectionor rate-sensing means to sense the deflection of aselected part, and cause the indications of such sensing means tocontinuously control the operation of an inertial torque producer, suchas a controllably rotatable flywheel, .which is attached to transmittorque to the selected part. Thus, if the sensor senses that theselected part has deflected in a clockwise direction around'the axis ofthe flywheel, the flywheel is caused to rotate clockwise, producingcounterclockwise torque reactions which reduce the deflection to zero.Since this action is localized at a given location, a number oflocations may be thus equipped, as determined by the conditions of thegiven situation, providing. correction over an entire structure.

In the most common situation, that a structure is elastically flexible,so that it tends to oscillate, the application of our invention providesdamping of such oscillations. The theoryof continuous beams teaches thebenefit of applying to a continuous flexible structure at variousdiscrete points torques tending to negate any deflection resulting fromexternally applied forces. That theory is, however, concernedprimarilywith continuously applied dead weight loading, and'thetorquesenvisaged are the reaction produced by holding the structure firmagainst rotation at selected points. However, theresults it teaches,that stresses in and deflection of the structure are thus reduced inmagnitude, appear as benefits in the practice of our invention also.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIGS. 1 and 2 represent, in two views, schematically an embodiment ofour invention;

FIG. 3 represents a more elaborate embodiment;

FIG. 4 represents an alternate device for inertially producing torque,for use in embodiments of our invention;

FIG. 5 represents schematically electrical means for use in theembodiment of FIGS. 1 and 2;

FIG. 6 represents'schematically electrical means for controlling theoperation of the device represented in FIG. 4;

FIG. 7 represents a modification of the embodiment represented in FIGS.1 and 2; i

FIG. 8 represents schematically electrical means for controlling theoperation of the embodiment represented in FIG. 7; and

FIG. 9 represents generally the extension of the application of ourinvention to a two-dimensional structure.

DESCRIPTIONOF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 represent aflexible mast 10, which may be an antenna, mounted upon a mobilevehicle. 12, whose rolling while in motion will necessarily cause themast to be oscillated at its base, which, in the absence of ourinvention, would produce shipping of large amplitude, as indicatedgenerally by the dashed outline 10A in FIG. 2. At the tip of mast 10there are represented a flywheel 14, and a gyroscopic rotation sensorl6, oriented to sense angular deflection of .the mast tip in a planenormal to the axis of flywheel 14. A motor 18 supports and 'drives theflywheel 14 in a direction determined by and the same as the angulardisplacement sensed by sensor 16. Thus, if the mast 10,-as a result ofrolling of vehicle 12 while in transit, tended tosway as represented bydashed outline 10A of FIG. 2, sensor '16, upon sensing the beginning ofthe deflection clockwise, as represented, would (through aservoamplifier system) cause. motor 18 to drive flywheel l4 clockwise,producing an inertially generated reaction torque on the. frame of motor18, andthrough it to the tip of mastl0tending toturn itcounterclockwise. This torque will bend the tip of mast l0counterclockwise, causing it to assume a position similar to thatrepresented by 10B. The total excursion of-the middle of the mastismarkedly reduced, and that of the tip rendered negligible by thisoperation of our invention; in ef-' feet, the mastappears stiffer thanit is in fact, and'the undesired deflection with respect to the base ofmast 10 of the controlled tipis markedly reduced;

Since mast 10 is an extensive structure, more than one point on it maybe selected for control. Thus FIG. 3representsin outline the deflectionto be expected by applying an additional flywheel 20, motor 22,andgyroscopic sensor 24 at the mid-, point of 10,-with the indicatedresult represented by 103.

For simplicity, the control has been represented as affecting onlytransverse deflection of the mast 10 with respect'to the long axis ofvehicle 12. It is, of course, possible to provide anotherflywheel-'motor-sensor combination with the respective axes of thevarious components orthogonal to thoseof the combination 14, 18 16,- tocontrol fore-and-aft' deflections as well, although the relativelygreater length of the wheelbase of a conventional vehicle compared withits track width is likely to rendersuch damping lessnecessary.

The use of a flywheel to produce torques inertially is convenient whereit may be expected (as in the example represented by FIGS. 1, 2, and 3)that the time average of the torque required, averaged with due respectto sign, will be zero. However, where this condition does not exist, thedevice represented by FIG. 4may be employed. Nozzles to serve as massejectors26 and 28 are spaced apart by a lever arm.

distance and oppositely directed. Operation of solenoid valve 30willpennit discharge of compressed gas from source 32 through nozzles 26 and28 into external space; the reaction produced upon the structure by theinertia of the gas being accelerated out of the noules will produce acounterclockwise torque. Similarly, nozzles 34 and 36, when caused todischarge gas by operation of solenoid valve 38, will produce aclockwise torque by reaction. Operation of one or the-other of solenoidvalves 30 and 38 will produce a torque in one or the other direction,just as will operation of motor 18 to accelerate flywheel 14 in one orthe other direction. Since in the.

motor 18 responsively to the indications produced by gyroscopic sensor16; and FIG. 6 represents a similar arrangement for controlling solenoidvalves 30 and 38 represented in FIG.

In FIG. 5, a potential divider 40 is represented as the sensor of theposition of gyroscopic sensor 16, so that the setting of the moving armof 40 is a measure of the angular displacement sensed by 16. Potentialdivider 40 has extreme ends of its resistor tied to the secondary of atransformer 42, the moving arm of 40 and the center tap of the secondaryof 42 being connected to input terminals of amplifier 44, whose outputis fed to phase-sensitive detector 46. The necessary reference voltagefor operation of phase detector 46 is provided by transformer 48, whoseprimary, in parallel with the primary of transformer 42, is fed from analternating source 50. Potential divider 40 is used conventionally asthe position pickoff for gyroscopic sensor 16; as its moving arm isrotated to one side or the other of the midpoint of its resistor, thephase of the AC potential from transformer 42 which is applied to theinput of amplifier 44 will change. Consequently the polarity of theoutput of phase detector 46 (which is provided with comparison potentialfrom transformer 48 which is in phase with the output of transformer 42)which appears at terminal points marked T-T will depend upon theposition of the moving arm of potential divider 40, and will thus causethe direction of rotation of motor 18 (here represented as apermanent'field commutator motor) to depend upon the position of themoving arm. Thus, if the central position of the moving arm of potentialdivider 40 corresponds to a vertical position of the tip of mast 10, thedirection of rotation of motor 18 will depend upon the direction inwhich the end of mast 10 has tilted.

FIG. 6 represents simply an alternative to motor 18 as a load forconnection to terminals T-T, comprising solenoid valves 30 and 38 ofFIG. 4, tied in parallel respectively through diodes 52 and 54 toterminals T-T. The opposite poling of diodes 52 and 54 obviously has theeffect that potential of one polarity applied to terminals T-T will openone valve, and potential of reversed potential will open the othervalve.

It is not pretended that the control circuitry of FIGS. 5 and 6represents sophistication; but it has the virtue that, with modernsemiconductor devices, it can readily be built compactly enough to behoused in situ with the motor and gyroscopie sensor, requiring only DCsupply.

FIG. 7 exemplifies the fact that various forms of displacement sensormay be employed in our invention. A projector 52 of a narrow beam oflightis represented fixed at the base of mast 10, aimed vertically. Twophotosensitive devices 54 and 56 are represented fixed on opposite sidesof the tip of mast 10, so that when mast 10 is erect and aligned withthe beam of light from projector 52, both 54 and 56 will be equallyilluminated, but when the mast is deflected, one will be illuminatedmore than the other. FIG. 8 represents schematically a mode ofconnection of photosensitive devices 54 and 56 to the two inputs to adifferential amplifier 58, whose output will depend in magnitude andpolarity upon the difference in illumination of 54 and 56. This outputappears at terminals marked T, T. Connection of these terminals to thesimilarly marked terminals of motor 18, as shown in FIG. 5, or of thesolenoid valve system represented in FIG. 6, will result in inertiallyproduced torques of the proper direction to negate deflection of the tipof mast l0, producing the same result as the arrangement represented bythe use of gyroscopic sensor 16in FIGS. land 2.

The sensors employed have been described generically as deflectionsensors; and the use, for example, of a freely rotatable gyroscope willcause the system to operate to cancel out deflections. It is well knownin the art to cause a gyroscope to function as a rate sensor. This isdescribed in Handbook of Automation, Computation and Control, Volume 3,editors Grabbe, Ramo, and Wooldridge, l96l, John Wiley and Sons, Inc.,New York City, N.Y., Library of Congress Card 58-10800, Chapter 28,pages 07-09; the so-called rate-integrating or displacement gyrosco e isdescribed immediately thereafter on pages 09-1 If a ra e sensor ISemployed In our invention, the effect of its operation will be moredirectly to damp out oscillations than to cancel deflections as such.Since, however, damping of oscillations will in general reducedeflections also, we have used the term displacement sensor to includeboth displacement rate sensors and displacment-rateintegrating sensors,since our invention may use either or both, according to the particularcharacteristics desired; and use damping of deflections" generically toinclude reduction of their amplitude, as well as damping ofoscillations.

For complete exemplification of the applicability of our invention, FIG.9 represents a structure 62 which is extensive in two dimensions whichis provided at various points with sensor-torque-producer unitsrepresented simply as rectangles 64 bearing the letter U to indicatethat each is a unit comprising a suitable sensor which controls theoperation of a source of inertially produced torque. It is, of course,evident that our invention may equally well be applied to athree-dimensional structure. While while we have taught and explainedour invention in application to a long flexible mast, which is apractically useful form of the embodiments which we have constructed anddemonstrated, it is evident that its principles are generally applicableto any flexible structure whose oscillations are to be damped or whichis otherwise to be given a simulation of greater rigidity than in factit possesses as a simple structure. It is also evident that, while wehave for simplicity shown embodiments in which the sensor is located atsubstantially the same point as the torque-producing means, it would,for example, in FIG. 7, be possible to mount the projector 52 at the tipof mast l0 pointing downward, and mount the photosensitive cells 54 and56 at the base of mast 10, so that the sensor device proper might beconsidered as being at least partially located away from this pointwhose deflection is controlled.

We claim:

1. Means for damping undesired deflections of an extensive structurewith respect to a selected reference point of the structure comprising,

means for sensing the angular deflection of a controlled point of thestructure with respect to the selected reference point, a source ofinertially produced torque, said source including a mass, means foraccelerating said mass to effect said inertially produced torque, saidsource providing a torque to said structure at the controlled pointresponsive to said sensing means to produce rotation in a directionopposed to said angular deflection.

2. The means claimed in claim I in which the said controllably operativesource of inertially produced torque is a flywheel driven by acontrollable motor.

3. The means claimed in claim 1 in which the said controllably operativesource of inertially produced torque comprises ejectors which areadapted to produce torque by the reactions produced by ejection of massfrom the ejectors into external space.

1. Means for damping undesired deflections of an extensIve structure with respect to a selected reference point of the structure comprising, means for sensing the angular deflection of a controlled point of the structure with respect to the selected reference point, a source of inertially produced torque, said source including a mass, means for accelerating said mass to effect said inertially produced torque, said source providing a torque to said structure at the controlled point responsive to said sensing means to produce rotation in a direction opposed to said angular deflection.
 2. The means claimed in claim 1 in which the said controllably operative source of inertially produced torque is a flywheel driven by a controllable motor.
 3. The means claimed in claim 1 in which the said controllably operative source of inertially produced torque comprises ejectors which are adapted to produce torque by the reactions produced by ejection of mass from the ejectors into external space. 